Oxidation Kinetics of WTe₂ Surfaces in Different Environments

Tungsten ditelluride, WTe2, a layered transition metal dichalcogenide (TMD), displays superior physical and electronic properties and offers a fertile playground to study physics in low-dimensional materials with nontrivial band structures. However, WTe2 oxidizes in the air, leading to the formation of a surface oxide layer that introduces disorder and deteriorates electronic charge transport. This surface oxide, therefore, suppresses the intrinsic properties of WTe2 and can lead to the degradation of device performance. In this study, we report the formation of surface oxide and its kinetics in WTe2 single crystals through a combination of atomic force microscopy (AFM), Raman spectroscopy, and ellipsometry measurements. The measurements reveal nonuniform surface oxide dynamics, which upon saturation after several hours of atmospheric exposure yields a self-limiting approximately 2.5-nm-thick amorphous surface layer. In addition, in a controlled environment involving a continuous flow of nitrogen (N2), the formation of surface oxide is considerably impeded. These results offer insight into the surface degradation mechanisms of WTe2, which should be taken into account when striving for the optimal design and performance of WTe2-based devices.